Electric signaling



June 11, 1929. w. A. PHELPS 1,717,062

ELECTRI C S IGNALING Filed July 31, 1926 lnvemor: Wa/fer A. Phelps flI/O/Wey Patented .lune -11, 1929.

1.11 .062- .UiNITED STATES PATENT OFFICE-.5

WALTER A. YHELPS, OF CLIFTON, NEW

' LABORATORIES, INCORPORATED, OF N YORK.

Application filed my 31,

ing and particularly to carrier current telegraph systems.

An object of the invention is to stabilize the operation of carrier current telegraph systems.

:A related object of the invention is to reduee distortion inf such systems and thereb increase the s ed of operation. A specific, o ject of the invention is to renderthe reception of signals substantially independent of changes inthe attenuation of the medium over which the signals are transmitted.

According to common practice in car rier current telegraph systems, a relay in the receiving circuit is thrown to its marking position by the action of rectified incoming carrier current, corresponding to dots and dashes. No-carrier current is received during a spacing interval, and the armature of the receiving relay is returned to its spac ing position by the action of a direct current through an auxiliary biasing winding of the relay. A multiplex carrier current telegraph system of this type is shown in Fig. of an article by Messrs. Qolpitts and Blackwell entitled Carrier current tale phony and. telegraphy published in the Transactions of the AmericanInstitute of Electrical Engineers, vol. 40,1921,

In systems of this type there is ,no constant relation between the restoring :torce on the armature of the receiving relay and the force which tends to'throw the armature to the marking position. The former varies only with variations in the voltage of a local battery at the receiving station, while the latter depends mainly on the attenuation of the line over which the signals are transmitted. The amplitude of the received carrier current varies appreciably in response to changes in the attenuatin properties of the transmission line while t e local biasing current remains una ected by such changes,

- thus tending to produce distortion in the signals which makes it necessary to .reduce the speed of operation of the system.

This difiiculty is largely overcome by means of the present invention by causing the restoring current through the biasing winding of the receiving relay to'vary approximately in the same-way as the incommg carrier currents. In carrym out the invention, the biasing winding 0 eachire- 'Assmnon 'ro BELL mminrnonn EW YORK, N. Y., a COBPQRATION or new ELnc'rn-Ic srelunme.

1926. Serial No. 126,233.

ceiving relay ata terminal is supplied with a current transmitted over the line with the telegraph signals, but 'throu h a separate nals and the biasing current. In this way the rectified current and'the biasing current will vary in a corresponding" manner with changing line conditions, thus. tending to eliminate bias in the received signals. According to a modification of the invention, a marking signal is transmitted by means of a carrier current of a particular frequency, and a spacing signal is trans.

'mitted by .means of a carrier current ofanother frequency. According to this method, each receivin relay at aterminal is thrown to ltsmar ing position, in the usual manner, by means of rectified incoming carrier current, and is restored to its spacing position by passing another rectified. lncommg carrier current through the biasing wind ng of the relay, any change in the transmission condition of the line afiecting both currents in substantially the same manner.

The various features of the invention will be described in connection with the acc'om-- panying drawing in which:

Fig. 1 is a diagrammatic illustration of a terminal of a multiplex carrier current telegraph system embodying the invention;

Figs. 2 and '3 show curves used in deicribiaig the operation of the system of Fig. n

Fig. 4 is a diagrammatic illustration of a modified system.

In Fig- 1 there is shown the east terminal of a multiplex carrier current telegraph system, the usual west terminal, which is identical to the-east terminal, being omitted for the 'sake'of simplifying the showing. The drawing shows only. so much of the Morse telegraph'equipment as is necessary for a complete understanding of the invention, this equipment being similar to that shown in Fig. 55 of the Colpitts and Black- RC connected to a common receiving c1r-' cuit RL. The commontransmitting circuit TL and the common receiving circuit 110 I practice the lower frequencies as a group are RL' are coupled to the multiples transmistheir frequencies,and according to common used for transmission from west to east, and the higher frequencies as a group are used for transmission from east to west.

Each transmitting channel includes a source of carrier current, a circuit for modulating the carrier current in accordance with signal impulses, and a selective cir cuit. These channels are identical in construction and hence detailed reference will becmade onlyto the apparatus of channel T 1' The out o'ing channel TC comprises an oscillator 5 a sending key 5, a sending re lay 6 and a transmitting selective circuit- TSQ. These elements are shown in detail in Fig. 55 of the Colpitts and Blackwell article, supra.- The selective circuits employed in the system may be either resonant circuits, or may be band filters of the type disclosed in Patent No. 1,227,113 to G. A. Campbell, issued May 22, 1917.' The oscillators 0,, 0 are adapted togenerate car- 'rier' currents of the different frequencies which are assi ned to the respective transmitting ehanne s.

Carrier currents of thefrequency assigned to the channel TC are normally transmitted from oscillator 0 through se lective circuit TSC common transmitting circuit TL, and transformer T to the multiplex transmission line ML. When the sending key 5 is opened the sending relay 6 is deenergized and the oscillator 0 is shortcircuited at the contact of the sending relay. The mani ulation of the sending key.5 thus controls tiie sending relay 6, which in turn impresses the signals on the outgoing carrier current. Carrier currents'of the frequencies assigned to other transmitting channels are similarly impressed upon the line ML. j

Each receiving channel includes a receiving selective circuit, an amplifier, a detector anda receiving relay. These channels are allidentical except, of course, that the constants ofthe selective circuits differ to the extent necessary-to accommodate the different frequency carrier currents employed. The receiving channel R0,, for example, comprises areceiving selective circuit RSC which may be a resonant circuit. or a band filter, an amplifier A a detector D and a receiving relay 3,. Carrier currents lncoming over the line 'ML are transmitted through transformer T to the common receiving circuit RL where they are picked up by the respective selective circuits for transmission to the proper channels. Cur-' rents of the frequency assigned to channel R0,, for example, are transmitted through selective circuit RSG are amplified and detected in the amplifier A and detector D and caused to actuate receiving relay R In addition to the signaling channels in- -dicated,,a control channel is also connected to the line ML, employing a frequency different from that of any of the signaling channels, for the purpose of supplying biasing current to the relays in all the receiving circuits. The channel. TC for transmitting the biasing current includes an oscillator B0 and a selective circuit TSC. The chanintervals when no carrier currents are received over the si naling channels. Under such conditions, t e armature of relay R for example, is moved to its "spacing position andthe associated sounder 9 isdeenergiZed. When carrier currents of the frequency assigned to channel RC are received, which is the condition shown in the drawing, space current is caused to flow in the output circuit of the detector 1) from grounded bat-- tery 10, through the primarywinding of transformer 11, upper windings of relay R to the plate of detector tube D and thence through the space discharge path to the grounded filament. The upper windings of relay R, carry a greater current than the lower biasing windings and are so poledv that the magnetic effect of the rectified current-flowing therein overpowers the magnetic effect produced by the biasing current and causes the armature of the relay to be moved to the marking position shown in 'the drawing.- When the armature of relay R is in this position, the sounder 9 is actuated by current flowing over a circuit extending from ground, through battery.12, armature of relay R winding of sounder 9, battery 13, to ground.

During a spacing interval when no carrier current is received in the channel RC the.

armature ofrelay R is moved to its spacing position by the action of the rectified current flowing continuously in the circuit including the space current path of detector D and the lower windings of all the receiving relays. The choke coil 8 serves to prevent signal currents in any receiving relay R or R from building up currents in the common v biasing circuit which. might afiect other receiving relays to which the biasing circuit isl'connected. The secondary winding ofthetransformer 11 is connected to thecentral'auxilia windings of.the relay .R and a change '0 vcurrentin this circuit causes a building u' of flux which accelerates the operation the relay, as is common practice in carrier te'lefiraphy.

It will be seenthat t e signaling currents and the biasing current are affected by the same transmission conditions on the line ML and hence that the rectified signaling currents and biasing current are caused to rise and fall together whenever theattenuating properties of the line ML vary due to changmg weather conditions, etc., thus tending to eliminate bias ii the received signals. The

operation of the system under changing line conditions is illustrated by i the. curves of Figs. 2 and 3. In Fig. 2, a signal originally signal, at the receiving terminal, assumes the form represented by the curve I). The enlarged curve 6 of Fig. 3 represents a'single dot signal such .as is received. for example, in the receiving channel R0,. Thejvalue of the rectified current produced by thisincoming signal is c, and the equivalent value of the biasing current is (Z. When the rectified signal current rises to the value d, the armature of the receiving relay 1s thrown over to its marking position, and when it falls again below this value the armature of the relay is restored to its spacing position by the action of the biasing current. A change in theattenuation of the line ML caums a change in the form of the signal I), a decrease in the line attenuation, for example, causing the signal to take the form indicated by the curve 9. If the biasing'c-urrent remains unchanged, receiving relay will be. actuated for the same current as before, and in such case the signal 'will be distorted by the amount ww-lryz. However, if the biasing current is also caused to rise, for example to the value h, due to the same conditions which cause the signalin current to rise, the length of the signal will then be m, which'is close to the originallength wy. The invention, therefore, by

' maintaining the signaling currents and'the current always in the proper relation biasin other, tends to eliminate the distortoeac tion heretofore caused by changes in the line attenuation.

' In carrying out the invention it is not necessary to decrease the number of communi'-, cation channels available withinv a given frequency range in order to add the two additional channels required for the purpose of transmitting biasing current in both directions over the line. Since no signals are I transmitted over these channels, only a very narrow band of frequencies is required, and these frequencies may beplaced in the usual dead'spa'ce between the two oppositely directed groups of signaling frequencies. For

example, in a multiplex system employing ten channels in one direction utilizing fre quencies lying between 3300 and 5500 cycles, and ten channelsin the opposite direction employing frequencies lying between 6500 and 10000 cycles, the biasing frequencies may lie in the frequency space between 5500 and 6500 cycles.

In the modified system illustrated in Fig.

4, a marking signal is transmitted bymeans ot a carrier current of one frequency and a spacing signal is transmitted by means ofa carrier current of another frequency. Themarking and spacing currents preferably lie close together in the frequency scale so that any change in line attenuation will affect both currents in substantially the same manner. This system requires two transmitting and two receivingchannels ateach terminal for each complete two-way trans mission. F urthermore, since it is necessary' to employ two frequencies for the transm sslon of signals In each direction instead ofone frequency as in the system described above, only half as many channels may be included in a given frequency range as' in the above system. This system, however,

provides a highly satisfactory method of transmission, since the quality of the signals is substantially independent of variations in lineattenuation, and may be employed to advantage when only a relatively small number of communication channels and high quality transmission are required.

In the system of Fig. 4, when the transmitting key 14 is closed,-as shown in the drawing, the upper winding of transmitting relay 15 is energized over a circuit extending from ground, through battery 16, upper Winding of relay 15, key 14, battery 17 to ground. Under such conditions, the lower contact of relay 15 is closed, thus short-circuiting the output of oscillator 0,, and the upper contact is open, thus permitting carrier current to be transmitted from oscillator 0,, through amplifier A,, transmitting selective circuit TSC transformer T to theiline ML. Although current is at alltimes 's'upplied to the lower winding of-relay 15-from battery 16, the upper winding of this relay carries a greater current than the-lower winding when the key 14 is closed, since the energizing circuit of the 'upper winding includes batteries 16 and 1 7 in series aiding,

' producing a' magnetic effectsufiicient toovercome that of the lower winding. The oscillator O furnishes the current for actuating the receiving relayat the distant to. minal to its marking position, and is-transmitting at all times when the key 14 is" 15 isactuated, opening its lower contact and thus removing a short circuit from the output of the oscillator O and closing its upper contact and thus short-circuiting the output of the oscillator 0,. The oscillator Q transmits spacing current through amplifier A "selective circuit TSC transformer T to the The marking current incoming over the line ML is selectively transmitted by the selective circuit ESQ, and is amplified and rectified in the detector-amplifier DA the rectified current energizing the upper winding of receiving relay 18 and thus attracting the armature of this relay to its marking position. The spacing current, of a different frequency, incoming over the line ML, is selectively transmitted through the selective circuit RSC and is amplified and rectified in the detector-amplifier DA the rectified current energizing the lower windingof the relay 18 to move the armature of this relay to its spacing position.

Although the invention has been descrlbed 'in connection with certain specific embodiments, it is also susceptible of numerous other applications without departing from the scope and spirit of the invention as'defined by the appended claims.

What is claimed is:

1. In a signaling system having a.translating device associated with a variable transmission medium .over which currents of different frequencies. are transmitted, the method of reducing distortion which comprises operating said device in one direction in response to current of a particular frequency, and continuously biasing said de vice in another direction in response to current of another frequency.

2. In a signaling system in which a recervmg relay 1s operated 1n one dlrection 1n response to a signaling current-traversing a conducting path having variable attenuating properties, and is operated in another direction in response to a biasing current,

the method of reducing distortion which.

'rents of a particular frequency, a control comprises subjecting said biasing current to substantially the same conditions causing attenuation as those affecting .the signaling current, whereby changes in the attenuation of said path will affect equally the signaling current and the biasing current.

3. In a signaling system having a plurality -of receiving relays associated with a variable transmission medium over which signaling 4 currents are transmitted, the

- another frequency.

method of reducing distortion which com.-

prisesoperating said relays in one direction in response to signaling currents comprised .witlnn mutually exclusive bands A of fre-' quencies, transmitting over said medium a bias control current and utillzmg said bias control current to operate said relays n common inanother direction.

4. A telegraph system comprising a medium over which currents of different frequencies are transmitted, a receiving relay, m ans for operating said relay from its spacing to its marking" position in response to current of a particular frequency, and

means for operating said relay from said marking position to said spacing position 1n response to current of another frequency.

5. A telegraph system comprising a medium over wlnch currents of different frequencies are transmitted, .a receiving relay having a mam winding and a bias ng wind- 'ing, means for energizing said main windgizing said biasing winding in response to current of another frequency.

, 6. A telegraph system comprising a medium over which currents of different-frequencies are transmitted, a receiving relay including a main winding and a biasing winding having a smaller number of ampere turns than said main winding, means for energizing'said main winding in response to current of a particular frequency, and means for continuously energizing said bias ing winding in response to current 'of 7. A- multiplex carrier current telegraph system comprising a medium over which carrier currents of different frequencies are transmitted, a plurality of receiving relays, means for operating said relays from their spacing to their marking positions in rechannel associated with said receiving circult for continuously receiving current of a frequency different from the signaling currents, and means for operating said devices in response to said control current when no signaling cur-rent is received by the associated' channel.

9. A multiplex carrier current telegraph system comprising a circuit for receiving currents "of different frequencies, a plurality of receivingchannels associated therewith, selective circuits for transmitting mutually exclusive bands of signaling frequencies to said channels, a detector in each of said channels, a receiving relay in ,each of said channels having a winding in the output of the detector'therein to actuate said relay to its marking position, a control channel associated with said receiving circuit for continuously receiving current of a frequency different from the signaling frequencies, a detector in said control channel, and an auxiliary winding oneach of said receiving relays connected to the output of said last mentioned detector, said auxiliary windingsbeing so proportioned and so'poled as to cause said relays to be returned to the spacing position when no signaling curquencies actuatin -two positions an the current of the other rent is received in the associated receiving channel. v

10. In a telegraph system employing a two-position relay, means to transmit current of one frequency controlled in accordance with signals, 'means to transmit current of another frequency to indicate spaces,

and means for actuating said relay under the v sole control of said currents of the two frequencies, the current of one of said frethe relay to one'of its mentioned frequency causing the relay to move out of such position into its other position.

In witness whereof I hereunto subscribe my name this th day of JulyA. D., 1926.

WAL'ILER A. PHELPS. 

